Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$88.52	12.234%	$99.3495	$99.35	$99.35	$99.30
Purchase #2	$59.28	5.272%	$62.4052	$62.41	$62.40	$62.40
Purchase #3	$210.82	6.205%	$223.9014	$223.90	$223.90	$223.90
Purchase #4	$160.65	7.259%	$172.3116	$172.31	$172.30	$172.30
Purchase #5	$150.63	6.584%	$160.5475	$160.55	$160.55	$160.50
Purchase #6	$83.26	12.375%	$93.5634	$93.56	$93.55	$93.60
Purchase #7	$195.75	9.489%	$214.3247	$214.32	$214.30	$214.30
7 purchase totals =	$948.91		$1,026.4033	$1,026.40	$1,026.35	$1,026.30